Hide NavigationViewItem Chevron if Children is empty

dev/NavigationView/NavigationViewItem.cpp

@@ -144,9 +144,16 @@ void NavigationViewItem::UpdateRepeaterItemsSource()
             }
             return MenuItems().as<winrt::IInspectable>();
         }();
+        m_itemsSourceViewChanged.revoke();
         repeater.ItemsSource(itemsSource);
+        m_itemsSourceViewChanged = repeater.ItemsSourceView().CollectionChanged(winrt::auto_revoke, { this, &NavigationViewItem::OnItemsSourceViewChanged });
     }
 }
+
+void NavigationViewItem::OnItemsSourceViewChanged(const winrt::IInspectable& /*sender*/, const winrt::NotifyCollectionChangedEventArgs& /*args*/)
+{
+    UpdateVisualStateForChevron();
+}
 
 winrt::UIElement NavigationViewItem::GetSelectionIndicator() const
 {
@@ -468,7 +475,7 @@ void NavigationViewItem::UpdateVisualStateForChevron()
 
 bool NavigationViewItem::HasChildren()
 {
-    return MenuItems().Size() > 0 || MenuItemsSource() != nullptr || HasUnrealizedChildren();
+    return MenuItems().Size() > 0 || (MenuItemsSource() != nullptr && m_repeater.get().ItemsSourceView().Count() > 0) || HasUnrealizedChildren();
 }
 
 bool NavigationViewItem::ShouldShowIcon()

dev/NavigationView/NavigationViewItem.h

@@ -100,6 +100,7 @@ class NavigationViewItem :
     bool HasChildren();
 
     void UpdateRepeaterItemsSource();
+    void OnItemsSourceViewChanged(const winrt::IInspectable& sender, const winrt::NotifyCollectionChangedEventArgs& args);
     void ReparentRepeater();
     void OnFlyoutClosing(const winrt::IInspectable& sender, const winrt::FlyoutBaseClosingEventArgs& args);
     void UpdateItemIndentation();
@@ -124,6 +125,7 @@ class NavigationViewItem :
 
     winrt::ItemsRepeater::ElementPrepared_revoker m_repeaterElementPreparedRevoker{};
     winrt::ItemsRepeater::ElementClearing_revoker m_repeaterElementClearingRevoker{};
+    winrt::ItemsSourceView::CollectionChanged_revoker m_itemsSourceViewChanged{};
 
     winrt::FlyoutBase::Closing_revoker m_flyoutClosingRevoker{};
     winrt::Control::IsEnabledChanged_revoker m_isEnabledChangedRevoker{};

dev/NavigationView/NavigationView_ApiTests/NavigationViewTests.cs

@@ -759,5 +759,70 @@ public void VerifyNavigationViewItemInFooterDoesNotCrash()
                 Verify.IsTrue(true);
             });
         }
+
+        [TestMethod]
+        public void VerifyExpandCollapseChevronVisibility()
+        {
+            NavigationView navView = null;
+            NavigationViewItem parentItem = null;
+            ObservableCollection<string> children = null;
+
+            RunOnUIThread.Execute(() =>
+            {
+                navView = new NavigationView();
+                Content = navView;
+
+                children = new ObservableCollection<string>();
+                parentItem = new NavigationViewItem() { Content = "ParentItem", MenuItemsSource = children };
+
+                navView.MenuItems.Add(parentItem);
+
+                navView.Width = 1008; // forces the control into Expanded mode so that the menu renders
+                Content.UpdateLayout();
+
+                UIElement chevronUIElement = (UIElement)FindVisualChildByName(parentItem, "ExpandCollapseChevron");
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Collapsed, "chevron should have been collapsed as NavViewItem has no children");
+
+                // Add a child to our NavigationView parentItem. This should make the chevron visible.
+                children.Add("Undo");
+                Content.UpdateLayout();
+
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Visible, "chevron should have been visible as NavViewItem now has children");
+
+                // Remove all children from our NavigationView parentItem. This should collapse the chevron
+                children.Clear();
+                Content.UpdateLayout();
+
+                Verify.IsTrue(chevronUIElement.Visibility == Visibility.Collapsed, "chevron should have been collapsed as NavViewItem no longer has children");
+            });
+        }
+
+        private static DependencyObject FindVisualChildByName(FrameworkElement parent, string name)
+        {
+            if (parent.Name == name)
+            {
+                return parent;
+            }
+
+            int childrenCount = VisualTreeHelper.GetChildrenCount(parent);
+
+            for (int i = 0; i < childrenCount; i++)
+            {
+                FrameworkElement childAsFE = VisualTreeHelper.GetChild(parent, i) as FrameworkElement;
+
+                if (childAsFE != null)
+                {
+                    DependencyObject result = FindVisualChildByName(childAsFE, name);
+
+                    if (result != null)
+                    {
+                        return result;
+                    }
+                }
+            }
+
+            return null;
+        }
+
     }
 }